Device comprising a number of superposed bucket conveyors for sorting flat objects

ABSTRACT

The device for sorting flat objects comprises at least one first conveyor consisting of buckets moving along a closed loop first path and a second conveyor, mechanically independent of the first conveyor, also consisting of buckets moving in a closed loop path and vertically superposed over the first path. Movement of both conveyors are synchronized by an electric shaft. Flat objects are transferred between conveyors by gravity.

The invention relates to a device for sorting flat objects comprisingbuckets into which the flat objects are loaded, each bucket being movedalong a path above a collection of sorting outlets towards which theflat objects are removed.

The invention applies more specifically to a postal sorting machine. Apostal sorting machine customarily consists of a single bucket conveyor,the buckets moving along a very long closed-loop path to serve a greatmany sorting outlets. To reduce the floor space occupied by such amachine, there has already been the idea of designing a number ofhorizontal levels on which the buckets move, these levels beingconnected to each other by a path portion of helical shape. However,this solution leads to problems with the tension of the chain thatdrives the movement of the buckets and the strains to which the chain issubjected are detrimental to the reliability of the machine.Furthermore, this solution entails very powerful conveyor drive which isexpensive.

The object of the invention is to overcome this drawback.

To this end, the subject of the invention is a device for sorting flatobjects comprising buckets into which the flat objects are loaded, eachbucket being moved along a path above a collection of sorting outletstowards which the flat objects are removed, this device comprising atleast one first conveyor consisting of buckets moving along a first pathin a closed loop and a second conveyor, mechanically independent of thefirst conveyor, consisting of buckets moving along a second path in aclosed loop superposed with the first path in a vertical direction, andbeing one wherein the movement of the buckets of the first conveyoralong the first path and the movement of the buckets of the secondconveyor along the second path are synchronized by an electric shaft andthere is a zone along the two paths where the flat objects in thebuckets of the second conveyor are transferred under gravity into thebuckets of the first conveyor.

With this arrangement, the load that has to be motorized is lower thanit is with a long conveyor, and this makes it possible to envisage aless powerful individual drive means for each conveyor. The reliabilityof the entire assembly is thereby improved because of the reduction inthe lengths of chain, and the times taken to get the individualconveyors up to speed and the times taken to stop them can be shortenedas far as possible, making it possible to improve the sorting rate.

Still other features and advantages will become apparent from readingthe description which follows of one embodiment of a device according tothe invention illustrated very diagrammatically in the single FIGURE.

In the FIGURE, the device 1 for sorting flat objects comprises a lowerconveyor 2 consisting of buckets 2A moving along a first path in aclosed loop and an upper conveyor 3 consisting of buckets 3A movingalong a second path in a closed loop superposed with the first path. Thetwo paths extend in approximately parallel respective planes.

The conveyor 2 serves first sorting outlets consisting of baskets suchas 2B placed on a first horizontal level and the conveyor 3 servessecond sorting outlets consisting of baskets such as 3B placed on asecond horizontal level located above the first level of sortingoutlets. In the figure, only a small number of buckets 2A, 3A andbaskets 2B, 3B have been depicted, but it is to be understood that thetotal periphery of each conveyor is covered with buckets. Conveyorscomprising 200 to 350 buckets are commonplace in postal sortingmachines.

The buckets 2A of the conveyor 2 are fixed to a bracket 2C which issuspended in the conventional way from a structure involving running andguide rollers on a rail which forms part of the structure of theconveyor 2 and which runs alongside the first conveying path. Therunning and guide structure of the conveyor 2 is coupled to a drivechain passing over a drive pulley 2D driven by a motor 2F and a returnpulley 2E which also tensions the chain.

The buckets 3A of the conveyor 3 are also fixed to another bracket 3Cwhich is suspended from a structure involving running and guide rollerson another rail forming part of the conveyor 3 and running alongside thesecond conveying path. The running and guide structure of the conveyor 3is coupled to another drive chain passing over a drive pulley 3D drivenby a motor 3F and a return pulley 3E which also tensions the chain.

Note that the movement of the chains in the conveyors 2 and 3 isessentially rectilinear so that the chains are not subjected tosignificant torsion. The conveyors 2, 3 have independent drives, thepower of which is designed to suit the length of chain that is to bedriven.

Each bucket such as 2A, 3A may consist of three compartments each ofwhich can contain a flat object placed edge-on in a position that isslightly inclined with respect to the vertical. Each compartment of abucket is equipped with an opening mechanism consisting of a moving flap(not depicted) which allows the flat object to be discharged simplyunder gravity.

The position of each of the buckets in a conveyor is monitored andcontrolled by electronic tags fixed to each bucket and by cells workingin conjunction with these electronic tags, for example of the inductivesensor type, distributed around the periphery of the conveyor. This typeof electronic tagging makes it possible to identify each bucket in allphases of operation of the conveyor (start-up, running up to speed,stopping), getting around the problems of bucket vibration. Eachconveyor 2, 3 is controlled by its own regulator to serve the sortingoutlets allocated to it in an independent way. What this means is thatthe rate of recirculation of the flat objects (that is to say objectsgoing round on the conveyor by more than one circuit) is relatively low.Specifically, the traffic on a bucket conveyor distributing to fewersorting outlets is lower than on a bucket conveyor distributing to agreater number of sorting outlets.

This sorting device is supplied with flat objects from one or more localcenters such as 4 which feed the flat objects only into the buckets 3Aof the upper conveyor 3. If the flat objects are bound for a sortingoutlet served by the lower conveyor 2, these objects are transferredfrom a bucket 3A of the conveyor 3 into a bucket 2A of the lowerconveyor 2 across a transfer zone 5. In this transfer zone, the movementof the buckets 2A and 3A of the conveyors 2 and 3 are synchronized by anelectric shaft. Under running conditions, the buckets of the twoconveyors are moved along at the same constant speed. Synchronization istherefore intended to compensate for any drift of one or other conveyorso as locally to obtain perfect vertical alignment of the buckets 2A andbuckets 3A so that flat objects can be transferred. This synchronizationmay be achieved by slaving the motors 2F and 3F on the basis of thepassage of the electronic tags of the buckets 2A and 3A past determinedpositions where cells such as 2G and 3G are located. These cells arearranged in the transfer zone and the transfer zone 5 is placed near themotorized pulleys 2D, 3D to make the slaving as responsive as possible.As can be seen in the figure, these two pulleys 2D, 3D are placed at thesame end of the device 1. In the transfer zone 5, the buckets 2A and 3Aof the two conveyors follow parallel paths which are very close togetherin a vertical plane to allow a flat object in a bucket 3A to betransferred simply under gravity into a bucket 2A. If a flat objectcannot be transferred into a bucket of the lower conveyor because thisbucket is already full, the flat object is recirculated on the upperconveyor. The same is true if the two conveyors are not synchronized.

As visible in the figure, the system 4 for feeding in flat objects islocated between the drive pulley 3D of the upper conveyor 3 and thetransfer zone 5, which allows the feed system not to feed flat objectsinto buckets of the conveyor 3 which are recirculating flat objectswhich have not already been discharged into the sorting outlets.

The rate at which flat objects can be fed into the device according tothe invention may be about 15% higher than the feed rate in a devicewhich has the same number of buckets but in which the buckets move injust one path. The feature of having a number of levels of sortingoutlets also allows a new sorting session to be begun just after theupper conveyor has been emptied of the flat objects from the previoussession. What is more, the lower conveyor 2 can sort the flat objects ofone session while the flat objects of the next session are in theprocess of being sorted in the upper conveyor 3. The layout of thedevice according to the invention therefore makes it possible to shortenthe waiting time between two sorting sessions.

The invention extends to a device with more than two superposedconveyors, for example with three conveyors. In the case of a devicewith three conveyors with buckets superposed in the vertical direction,it is necessary to provide a transfer zone with an electric shaftbetween the uppermost conveyor and the lowermost conveyor and anothertransfer zone with an electric shaft between this uppermost conveyor andthe conveyor at the intermediate level, to prevent the latter frombecoming overladen by the transfer of flat objects.

What is claimed is:
 1. A device for sorting flat objects (6) comprisingat least one first conveyor (2) consisting of buckets (2A) moving alonga first path in a closed loop and a second conveyor (3), mechanicallyindependent of the first conveyor, consisting of buckets (3A) forreceiving flat objects moving along a second path in a closed loopsuperposed with the first path in a vertical direction, and being onewherein the movement of the buckets (2A) of the first conveyor along thefirst path and the movement of the buckets (3A) of the second conveyoralong the second path are synchronized by an electric shaft and there isa zone (5) along the two paths where the flat objects in the buckets ofthe second conveyor are transferred under gravity into the buckets ofthe first conveyor.
 2. The device as claimed in claim 1, in which thefirst and second conveyors (2, 3) each comprise a chain for driving thebuckets, the chain being mounted on a motorized pulley (2D, 3D), inwhich the motorized pulley of the first conveyor and the motorizedpulley of the second conveyor are placed at the same end of the deviceand the zone (5) for the transferring of the flat objects is near themotorized pulleys of the first and second conveyors.
 3. The device asclaimed in either of claims 1 and 2, in which each bucket (2A, 3A)carries an electronic tag and in which the electric shaft consists ofcells (2G, 3G) operating in conjunction with the electronic tagsbelonging to the buckets, these cells being arranged in the transferzone (5).